Etching method



Oct. 31, 1961 N. c. BRIDWELL ETCHING METHOD 3 Sheets-Sheet 1 Filed April 18, 1958 DRY AND HEAT- HARDEN REMAINING PORTIONS OF SECOND COATlNG ETCH EXPOSED PORTIONS OF METAL PLATE INVENTOR. NoRMANCBmDwELL BY &

KEY

NOT DARKENED m pm coATmG ATTORNEYS DARKENED PLASTIC COATING Oct. 31, 1961 Filed April 18, 1958 APPLY LIGHT smsmvE COATING TO METAL BASE PLATE.

EXPOSE COATING TO LIGHT IN A DESIRED PATTERN.

' WASH UNEXPOSED COATING PORTIONS FROM PLATE.

DRY AND HEAT HARDEN REMAINING COATING PORTIONS.

ETCH EXPOSED PORTIONS OF METAL PLATE.

WASH ETC HANT FROM PLATE BREAK AWAY OVERHANGING PORTIONS OF COATING N. c. BRIDWELL 3,006,796

ETCHING METHOD 3 Sheets-Sheet 2 I! I IIIIIIIII .7 FIEE I .7

INVENTOR. NORMAN C BRIDWEL L DARKENED PLASTIC comma KEY 6 NOT AR ENED m PLAS'IPIC EA I G M Oct. 31, 1961 N. c. BRIDWELL 3,006,796

ETCHING METHOD Filed April 18, 1958 3 Sheets-Sheet 3 APPLY SE D L1G HT SEN COATING O LA EXPOSE SECO COATING TO Ll [DENT AN TE ANG WAS NEXPOSED PORT] 5 OF SECOND COATING FROM PLATE.

INVENTOR. NORMAN C. Bm DWELL N DARKENED PL TIC COATlNG United States Patent Office 3,006,796 Patented Oct. 31, 1961 3,006,796 ETCHING METHOD Norman C. Bridwell, Washington Township, Lucas County, Ohio, assignor, by mesne assignments, to .gmes Graphic Products of Ohio, Inc., a corporation of bio Filed Apr. 18, 1958, Ser. No. 729,399 4 Claims; (Cl. 156-13) This invention relate to an etching method, and, more particularly, to a multi-stage etching method where a light sensitized coating is applied to walls of a pocket in a metal plate, and the coating is partially exposed to light and heat hardened to prevent or delay lateral attack of such walls during a subsequent etching step.

It has been found (see US. Patent 2,801,445) that a perforate, deposited latex article can be produced by dipping, in a suitable latex, an appropriately shaped form having a plurality of spaced pockets in the surface thereof, each of which pockets has a cross-sectional area which is a direct function of distance below the surface of the form, and then inductively heating the form. Inductive heating of the form causes rapid expansion of air entrapped in the pockets. The rapid expansion of air causes rupture of the latex which bridges the opening of the pocket. Upon rupture of the latex, surface tension thereof causes the unsupported latex film over the opening of each pocket to draw into a ring and, in essence, to form a reinforcing area of greater than original latex thickness around each of the pocket openings of the form. As a consequence, the finally cured latex article is pervious to air as well as to other gases, and is, therefore, suitable for use in contact with the human body, for example as an undergarment, but the perforations which make the article pervious are reinforced to such an extent that they do not constitute points of weakness of the article.

Although various attempts have heretofore been made to provide dipping forms having a desired number of pockets of a shape appropriate for use in producing perforate deposited latex articles in the manner described above, no satisfactory way had heretofore been discovered for forming the required pockets in the forms. Drilling, plating and etching techniques had all proved unsuccessful.

The instant invention is based upon the discovery of a new etching method, which method is suitable for commercial use in forming such pockets, for example in stainless steel sheets or plates. It has been found that plates so etched, when appropriately fabricated, constitute excellent dipping forms for use in the production of perforate, deposited latex articles.

It is, therefore, an object of the invention to provide an improved etching method,

It is a further object of the invention to provide a method which enables etching of pockets which increase from a predetermined maximum cross section at the surface of a sheet to a greater cross section below the surface of the sheet.

It is another object of the invention to provide an etching method which includes the steps of applying a light sensitized coating to a base sheet having a partially formed pocket, exposing portions of the coating to light, removing unexposed portions of the coating from the base, and then carrying out further etching to complete the pockets.

Other objects and advantages will be apparent from the description which follows, reference being made to the accompanying drawings, in which- FIG. 1 is a fiow diagram representing the several steps in a method according to the invention for producing, by

etching techniques, a plate having pockets of a predetermined cross-sectional area at the plate surface and an increased cross-sectional area at points below the surface;

FIGS. 2 through 10, inclusive, are cross-sectional views through a plate, and show the appearance of the plate at various stages in the method set forth in FIG. 1; and

FIG. 11 is a partially schematic view showing a tilted top rotating table which is convenient-1y used in carrying out an exposure to light of a second sensitized coating, which exposure constitutes one of the steps in the method of FIG. 1.

Referring now in more detail to the drawings, and specifically to FIG. 1, which is a flow diagram beginning on the first sheet of the drawings, continuing on the second sheet, and concluded on the third sheet, the several steps in etching a metal plate to produce pockets of the shape defined above are as follows:

(1) Application of a light sensitive coating material to a metal base plate;

(2) Exposure of the coating to light in a desired pattern;

(3) Washing of unexposed coating portions from the plate;

(4) Drying and heat hardening (if necessary) of remaining or exposed coating portions;

(5) Etching of exposed portions of the metal plate to form pockets;

(6) Washing of etchant from the plate;

(7) Breaking away of coating portions which overhang etched pockets;

(8) Application of a second light sensitized coating to the plate;

(9) Exposure of portions of the second coating to light;

(10) Washing of unexposed portions of the second coating from the plate;

(11) Drying and heat hardening (if necessary) of remaining portions of the second coating; and

(12) Additional etching of exposed portions of the metal plate.

The several steps in the method will be understood readily from the following example, which sets forth the best presently known method for practicing the invention, but is intended only as illustrative thereof, and in no way as limitative. The terms percent and parts, as used herein and in the appended claims, refer to percent and parts by weight, unless otherwise indicated.

Example A methyl methacrylate-polyvinyl alcohol dispersion sensitized with ammonium dichromate was applied to a stainless steel sheet. The stainless steel was A.I.S.I. type No. 430. The coating was applied by pouring onto the sheet, while the sheet was positioned on a platform which was rotating at approximately 80 revolutions per minute, and a stream of air at a temperature of about 120 F. was directed against the coating on the sheet to effect drying thereof. The resulting structure, after this first step in the method, is shown in FIG. 2, the stainless steel sheet being designated 15, and the light sensitized coating being designated 16.

The particular light sensitized coating composition which was applied to the sheet 15 was produced as follows:

A charge of 625 milliliters of methyl methacrylate monomer which had been freshly washed with a 20 percent solution of sodium hydroxide in water to remove hydroquinone, which is a polymerization inhibitor, was placed in a first container. A 3381 milliliter charge of a 10 percent dispersion of polyvinyl alcohol in water was heated to C. and placed in a second container. The

particular polyvinyl alcohol employed was 86 to 89 percent hydrolized, and had a comparatively low molecular weight as indicated by a viscosity, in a 4 percent water solution at 20 C., of 4 to 6 centipoises. The polyvinyl alcohol dispersion was flowed by gravity from the second container, through a pipe, through a 750 cc. capacity homogenizer, and was circulated back to the second container by the pumping action of the homogenizer. Methyl methacrylate monomer was flowed by gravity from the first container through a second pipe and into the stream of polyvinyl alcohol'dispersion flowing from the second container. to the homogenizer. By adjustment of valves in the pipe from the first container and in the pipe from the second container to the homogenizer, the rates of flow of the methyl methacrylate monomer and of the polyvinyl alcohol dispersion were adjusted to about 30 cc. per minute and 150 cc. per minute, respectively, until the homogenizerwas filled with polyvinyl alcohol dispersion and methyl methacrylate monomer. The homogenizer was then driven at approximately 8,000 revolutions per minute to homogenize the liquids and to circulate liquid from the homogenizer back to the second container. A 2 milliliter portion of a 30 percent hydrogen peroxide solution was then added to the second container, at which time the liquid temperature in the homogenizer was found to be 65 C. The homogenizer was then slowed to 4,000 revolutions per minute. Four additional 2 milliliter portions of the hydrogen peroxide were made to the liquid in the second container at two minute intervals. The temperature of the liquid in the homogenizer was observed to be 72 C. at the time the fifth hydrogen peroxide addition was made. When all of the methyl methacrylate monomer had been added to the system from the first container, the valve in the line from the first container was closed to prevent introduction of air into the system. The temperature of the liquid in the homogenizer was found to increase rapidly to 84 C. approximately 12 minutes after the first hydrogen peroxide addition, and then to drop to about 82 C. approximately minutes later, at which time the homogenizer speed was increased to 8,000 revolutions per minute. The temperature therein then increased to about 87 C. in an additional 15 minutes, after which time a uniform dispersion having a milky appearance was removed from the system. This dispersion had a viscosity of 275 centipoises at 80 F., a pH of 5.1, and a density of 60 Baum at 60 F. The dispersion was diluted with about 800 cc. of distilled water to a viscosity of 29.0 centipoises at 80 F. A 3595.3 milliliter portion of the resulting dispersion was made light sensitive by adding thereto a 190 milliliter portion of a dichromate solution which had been prepared by dissolving a 0.073 pound portion of ammonium dichromate in 0.048 gallon of distilled water heated to 130 F. and, after dissolution of the ammonium dichromate, cooled to 80 F. and adjusted to a density of 121 Baum by addition thereto of distilled water at 80 F. The resulting dichromated dispersion Was then dyed by mixing therewith 36 grams of Eosin Y per gallon of dispersion.

As a second step in the method, the light sensitized coating 16 was exposed to light in a desired pattern. Specifically, most of the coating 16 was exposed through a photographic positive which was transparent except for opaque dots having a diameter of about 0.007". The positioning of the opaque dots can be defined by reference to two groups of imaginary, parallel lines on the photographic positive, the spacing between successive lines in each group being 0.030, and the angle between lines in one group and lines in the other group being 60; the center of an opaque dot is at each intersection of these imaginary lines. Upon exposure to light, the dyed coating underwent a color change, which was a darkening, and was made insoluble in water. Exposed portions of the coating are designated 17 in FIG. 3, and

are dotted to indicate exposure and darkening, while a central portion of the coating, which was protected against exposure, is designated 16, and is represented in the same manner as the coating 16 in FIG. 2.

As the third step in the method, unexposed coating portions 16 were washed from the plate 15 by spraying water at a temperature of about 100 F. over the entire plate, while rubbing the surface lightly with a wad of absorbent cotton. A fragment of the plate 15 with exposed coating portions 17 adhering thereto, and after unexposed coating portions 16 have been washed away, is shown in FIG. 4.

As a fourth step in the method, the entire plate 15 and exposed coating portions 17 was then placed in an oven and heated to a coating surface temperature, as indicated by a contact pyrometer, of 500 F. Such heating dried the exposed coating portions 17, and increased their resistance to acids and other etchants, but did not appreciably change the appearance of the structure, which was essentially the same as that shown in FIG. 4.

As a fifth step in the method, the plate with the dried and heat hardened exposed coating portions thereon was etched in a splash-type etching machine. The plate was supported, with the coated side down, above a bath of 42 Baum ferric chloride solution. Paddles mounted on suitably journaled shafts were driven to splash the etchant against the lower surface of the plate. The plate was subjected to the action of the etchant for about 8 minutes, and was rotated about its generally'vertical axis at 2 minute intervals during etching. At the end of this etching step,'generally hemispherical pockets, one of which is designated 18 in FIG. 5, has been etched in the sheet 15. The diameters of the pockets 18 were about 0.015", because the etchant had attacked the metal laterally as well as perpendicularly. As is shown in FIG. 5, the pockets 18 extended under a part of the exposed, dried, and hardened coating '17 because of the lateral etching.

As a sixth step in the method, the plate was washed to remove etchant, and, as a seventh step, the overhanging portions of the exposed, dried and hardened coating 17 were removed to produce the structure shown in FIG. -6. Removal of the overhanging coating portions was accomplished by rubbing the plate briskly with a solid felt block.

As an eighth step in the method a second coating of the previously identified light sensitized coating material was applied over the exposed portions of the metal plate 15 and the remaining hardened coating portions 17, using the same technique as .in carrying out the first step of the method, as described above. As is shown in FIG. 7, after the eighth step had been completed, the portions of the sheet 15 which were exposed after the'first etching (step 5), and the portions of the hardened coating 17 which remained after breaking away of the overhanging parts thereof (step 7), were covered by a light sensitized layer 19 of the methyl methacrylate-polyvinyl alcohol material, which layer is designated 19. It will be noted that the portion of the layer 19 which is within the pocket 18 is represented as somewhat thicker than the rest of the layer 19. This is believed to be the actual situation, since the pockets 18 tend to trap the coating material, which is free to flow from the planar portions of the structure under the action of centrifugal force resulting from the rotation of the sheet 15. Since the thickness of the coating '19 is of the order of about 0.002", however, actual measurement of variations in coating thickness is extremely difiicult.

As a ninth step in the method, portions of the coating 19 were exposed to light. Such exposure was carried out using a fixture which is shown schematically in FIG. 11, and is generally designated 20. The fixture 20 comprises a top 21 suitably mounted on a drive shaft 22, which is journaled in a bearing 23. Th bQ t ug 23 is pinned to ears 24 which are welded or otherwise rigidly attached to a table portion 25. The table portion 25 is supported on legs 26, to which cross members 27 are welded or otherwise rigidly attached. A motor 28 is mounted on the cross members 27. A gear reduction box 29 is driven by the motor 28, and, in turn, rotates the shaft 22 and the top 21 at a rate of about one revolution per minute.

In carrying out the ninth step of the method, the sheet 15 with exposed and hardened coating portions 17 and the unexposed layer -19 was placed on the top 21, held fiat thereon, and exposed to light from a source 30. The source 30 supplied a generally horizontal beam of light, as indicated in FIG. 11 by the lines from the source 30 to the top 21, which light was incident at an angle of about 15 to the upper flat surface of the plate. The sheet 15 and applied coatings were rotated by the fixture 20 at the indicated rate during exposure, which was continued for approximately 8 minutes. The condition of the structure on completion of the ninth step of the method is shown in FIG. 8. Portions of the layer 19 in the bottoms of the pockets 18 remained unexposed and water soluble, while portions 31 thereof were exposed and insolubilized by light from the source 30.

As a tenth step in the method, unexposed layer portions 19 were then washed from the plate 15. This washing was accomplished by immersing the entire assembly in water at about room temperature for minutes, and then spraying with water at a temperature of about 100 F. For removal of the layer portions 19, however, abrasion with absorbent cotton was relatively ineffectual, since all the material to be removed was at the bottoms of the pockets 18. The condition of the plate after completion of the tenth step of the method is shown in FIG. 9.

As an eleventh step in the method, the layer portions 31 were dried and heat hardened by placing the entire assembly in an oven and heating until the surface temperature of the portions 31, as indicated by a contact pyrometer, reached 500 F. The appearance of the plate and adhered coating portions was not appreciably changed by this drying and heat hardening step, and was, therefore, essentially the same as that shown in FIG. 9.

As a twelfth and final step in the method, the sheet 15 and adhered coating portions 17 and 31 was then subjected to the action of a ferric chloride-hydrochloric acid etchant solution in the same manner as previously described in connection with the fifth step of the method, except that etching was continued for about 40 minutes. The etchant solution was prepared by mixing 400 cubic centimeters of 37 percent hydrochloric acid per gallon with 42 Baum ferric chloride solution. During the initial stages of this second etching step, only the surfaces of the metal which bounded the lower portions of the pockets 18 were subjected to the action of the ferric chloride solution. However, as etching proceeded, lateral attack also occurred, and, eventually, also upward attack, until pockets which are designated 32 in FIG. were formed. The pockets 32 were generally the shape of a part of a slightly flattened sphere having a diameter of 18 to 20 thousandths of an inch, and extending a total of about thousandths of an inch below the upper surface of the sheet 15. The upper surface of the sheet 15 was in a plane at right angles to the vertical axis of the pockets 32.

The etched sheet 15 with adhering coating portions 17 and 31 was then removed from the etching machine, washed, dried, and treated in hot methylene chloride to soften the adhered coating. After about a 15 minute immersion in the methylene chloride, the sheet 15 was removed and the softened coating portions were scrubbed therefrom with a brush, using a hot detergent solution to aid in the removal.

Dipping forms fabricated from plates etched as described have been used in the manufacture of deposited latex articles cured by dielectric heating as described above, and have been found to be entirely satisfactory, producing deposited latex articles with a plurality of perforations corresponding in position with the pockets 32 in the sheets 15 from which the dipping forms were fabricated.

Referring again to the first step of the method, the application of a light sensitive coating material to a metal base plate, neither the identity of the coating applied nor of the base plate to which the coating is applied is critical. The coating must be one which has sufficient resistance to whatever etchant is used in the fifth step that it prevents attack of the metal plate at points where attack is not desired. The coating must also be one to which a second coating of either the same or a different material will adhere in the eighth step of the method, and which Will withstand whatever processing is necessary to convert the second coating to a hardened condition in which it is resistant to a suitable etchant. A coating material produced as described above meets all of these requirements, and is also suitable for use in the eighthstep, as are other similar coating materials produced from methyl methacrylate or another acrylic monomer and a polyvinyl alcohol dispersion where the acrylic monomer and the polyvinyl alcohol are reacted in proportions ranging from about 0.7 part to about 2.5 parts of the acrylic monomer per part of the polyvinyl alcohol. Of course, the first coating can be removed from the metal sheet after completion of the first etching step, and, then, any known light sensitized coating composition which has the requisite acid resistance can be used in the first step of the method, or the partially formed pockets 18 can be pro duced by drilling, or in any other suitable way.

The coating material which is used in the eighth step of the method must be capable of forming a tightly adhering protective coating at all points where a flat surface, whether of the coating 17 (FIG. 5) or of the metal sheet 15 (in the case where the first coating is removed) adjoins the walls which define the pockets 18. The previously identified reaction products of an acrylic monomer and a polyvinyl alcohol have this characteristic, and are admirably suited for use in practicing this step of the method.

When the light sensitized coating used in practicing the method is one which has sufficient resistance to the action of an etchant after being exposed to light, steps 4 and 11 of the method can be eliminated. These steps, Nos. 4 and 11, are drying and heat hardening of the exposed portions of the light sensitive coating. In the foregoing example, each of these steps involved a heating of the sheet 15 and adhered coating portions until the surface temperature of the coating portion being dried and hardened reached 500 F.

Exposure of portions of the second coating to light, the ninth step in the method as previously set forth in detail, must be carried out in such a manner that the exposing light is incident at an acute angle to the major surface of the coating. The exposure, then, extends only partially into the pockets 18. The depth that the exposed portion of the second coating extends into the pockets depends upon the angle of the incident light. In the specific instance described in the example, the light was incident at about 15. By increasing the angle at which the light is incident, a deeper exposure can be accomplished, with the result that deeper pockets having larger diameters can be etched before erosion of metal adjacent the upper surface of the sheet 15 begins. Similarly, by reducing the angle of the incident light, shallower exposed coating portions are achieved, and less etching can be carried out before erosion begins adjacent the top of the sheet. The precise angle between incident light and the major surface of the sheet depends upon the result desired, and the ratio of lateral etching to depth of etching for the particular metal-etchant system. In any event, the angle must be acute, and must be such that only a part of the coating is exposed to light, and thereby insolubilized. Also, the angle must be suflicient that at least an appreciable por- 7 7 tion of the coating on the etched walls is exposed and insolubilized. v

It will be. apparent that various changes and modifications can be made from the specific details shown in the attached drawings and discussed in connection therewith withoutdeparting from the spirit and scope of the appended claims, and that, in its essential details, the instant invention comprises applying, to a metal plate having a partially formed pocket extending below a majority surface thereof, a continuous layer of a lightsensitized composition, which layer covers the major surface of the plate and the walls which define the pocket, exposing to light and insolubilizing a portion of the coating which covers the walls defining the pocket, while preventing exposure of at least one other portion of the coatingwhich cover such walls, washing unexposed coating from the plate to expose bare metal, and subject ing the exposed metal to the action of anetchant therefor. a

What I claim is: a a

1. A method for controlling the configuration of an etched pocket in a metal plate which comprises applying to a metal plate having a partially formed pocket extending below a major surface thereof a continuous layer of a light-sensitized coating composition, which layer covers the major surface of the plate and the walls which define the pocket, the coating composition being an aqueous dispersion comprising from percent to 25 percent of a thermal reaction product of from 0.7 part to 2.5 parts of an acrylic monomer and one part of a partially hydrolyzed polyvinyl alcohol, insolubilizing a portion of the coating which covers the walls defining the pocket, while preventing exposure of at least one other portion of the coating which covers such walls, by exposing the coating to light incident from a plurality of sides of the plate at an acute angle greater than zero relative to the coated major plate surface, washing unexposed coating from the plate to expose bare metal, and subjecting the exposed metal to the action of an etchant therefor.

, 2. A method for controlling the configuration of an etched pocket in a metal plate which comprises applying to a metal plate having a partially formed pocket extending below a major surface thereof a continuous layer of a light-sensitized coating composition, which layer covers the major surface of the plate and the walls which define the pocket, the coating composition being an aqueous dispersion comprising from 5 percent to 25 percent of a thermal reaction product of from 0.7 part to 2.5 parts of an acrylic monomer and one part of a partially hydrolyzed polyvinyl alcohol, insolubilizing a porportion of the coating which covers such walls, by exposing the coated plate to light incident at an acute angle greater than zero relative to the coated major plate surface, washing unexposed coating from the plate to expose bare metal, and subjecting the exposed metal to the action of an etchant therefor.

3. A method for controlling the configuration of an etched pocket in a metal plate which comprises applying to a metal plate having a partially formed pocket extending below a major surface thereof a continuous layer of a light-sensitized coating composition, which layer covers the major surface of the plate and the walls which define the pocket, insolubilizing a portion of the coating which covers the walls defining the pocket, while preventing exposure of at least one other portion of the coating which covers such walls, by exposing the coated plate to light incident at an acute angle greater than zero relative to the coated major plate surface, washing unexposed coating from the plate to expose bare metal, and subjecting the exposed metal to the action of an etchant therefor.

4. A method for controlling the configuration of an etched pocket in a metal plate which comprises applying to a metal plate having a partially formed pocket extending below a major surface thereof a continuous layer of a light-sensitized coating composition, which layer covers the major surface of the plate and the walls which define the pocket, exposing the coated major plate surface to a light source spaced therefrom which emits a beam of light that is incident to said surface at an acute angle greater than zero, rotating the plate about an axis normal to the coated major plate surface to insolubilize a portion of the coating which covers the upper portion of the walls defining the pocket, while preventing exposure of at. least one other portion of the coating which covers the lower portion of such walls, washing unexposed coating from the plate to expose bane metal, and subjecting the exposed metal to the action of an etchant therefor.

References Cited in the file of this patent UNITED STATES PATENTS 667,898 Wilcke Feb. 12, 1901 1,903,778 Conroy Apr. 18, 1933 2,854,336 Gutknecht Sept. 30, 1958 

1. A METHOD FOR CONTROLLING THE CONFIGURATION OF AN ETCHED POCKET IN A METAL PLATE WHICH COMPRISES APPLYING TO A METAL PLATE HAVING A PARTIALLY FORMED POCKET EXTENDING BELOW A MAJOR SURFACE THEREOF A CONTINUOUS LAYER OF A LIGHT-SENSITIZED COATING COMPOSITION, WHICH LAYER COVERS THE MAJOR SURFACE OF THE PLATE AND THE WALLS WHICH DEFINE THE POCKET, THE COATING COMPOSITION BEING AN AQUEOUS DISPERSION COMPRISING FROM 5 PERCENT TO 25 PERCENT OF A THERMAL REACTION PRODUCT OF FROM 0.7 PART TO 2.5 PARTS OF AN ACRYLIC MONOMER AND ONE PART OF A PARTIALLY HYDROLYZED POLYVINYL ALCOHOL, INSOLUBILIZING A PORTION OF THE COATING WHICH COVERS THE WALLS DEFINING THE POCKET, WHILE PREVENTING EXPOSURE OF AT LEAST ONE OTHER PORTION OF THE COATING WHICH COVERS SUCH WALLS, BY EXPOSING THE COATING TO LIGHT INCIDENT FROM A PLURALITY OF SIDES OF THE PLATE AT AN ACUTE ANGLE GREATER THAN ZERO RELATIVE TO THE COATED MAJOR PLATE SURFACE, WASHING UNEXPOSED COATING FROM THE PLATE TO EXPOSE BARE METAL, AND SUBJECTING THE EXPOSED METAL TO THE ACTION OF AN ETCHANT THEREFOR. 